Thermoplastic polymers are commonly used to manufacture various shaped articles that may be utilized in applications such as automotive parts, food containers, signs, and packaging materials. Shaped articles may be prepared from polyester by a number of melt extrusion processes known in the art, such as injection molding, compression molding, blow molding, and profile extrusion.
The most common polyester currently used is polyethylene terephthalate (PET). Due to recent trends toward sustainability and reduced use of petroleum, alternatives to PET are being investigated. Poly(trimethylene terephthalate), herein abbreviated 3GT, also referred to as PTT or polypropylene terephthalate, may be useful in many materials and products in which polyesters such as PET are currently used, for example molded articles. 3GT has properties including a semi-crystalline molecular structure.
British Patent 578097 disclosed the synthesis of 3GT in 1941. 3GT may be prepared using 1,3-propanediol derived from petroleum sources or from biological processes using renewable resources (“bio-based” synthesis). The ability to prepare 3GT from renewable resources makes it an attractive alternative to PET. 3GT produced from renewable sources of 1,3-propanediol is commercially available from E. I. du Pont de Nemours and Company (DuPont) under the tradename SORONA. DuPont pioneered a way to produce the 1,3-propanediol from renewable resources including corn sugar.
3GT may be modified with nucleators. For example, U.S. Pat. No. 6,245,844 discloses 3GT nucleated with a monosodium salt of a dicarboxylic acid selected from monosodium terephthalates, monosodium naphthalene dicarboxylates, and monosodium isophthalates. Other nucleators include salts of fatty acids, such as the sodium salt of montanic acid.
Nucleated 3GT polyesters containing mono-sodium terephthalate exhibit short crystallization half times and early onsets of crystallization as measured by differential scanning calorimetry (DSC) in cooling cycle tests. These are desirable effects because the nucleated polymers may quickly become rigid, leading to faster demold times and shorter cycle times in processing the polymers into shaped articles by such methods as thermoforming, injection molding, and blow molding. In addition, 3GT polyester containing mono-sodium terephthalate exhibited significant improvement in brittleness, heat resistance, and impact resistance over the non-nucleated 3GT.
Previously, toughening polyester has been achieved using an ionomer modifier, an epoxide-containing copolymer such as ethylene/n-butyl acrylate/glycidyl methacrylate (EBAGMA) (see WO85/03718) or a combination of ionomer and an epoxide-containing copolymer (see U.S. Pat. No. 5,091,478). The modifiers provided increased toughness and lower flex modulus, but the viscosity of the blends was increased, possibly due to reaction with the EBAGMA.
Despite the improvement in impact resistance found with nucleated 3GT, it is desirable to obtain 3GT compositions with even greater improvement in properties such as reduced stiffness (as demonstrated by lower Young's modulus) and impact resistance or toughness. Another desirable feature would be to reduce, or at least not increase, viscosity of the resultant blend in comparison with the nucleated 3GT.